I have a 2000 Dakota with 4.7 V-8 and what started with a "no bus" problem last year has returned. The PCM was replaced in June and everything was fine until last week. The engine died and the no bus appeared in the odometer again. I checked all the 5-V sensors and it never changed so I had the PCM replaced under warranty. Installed the new PCM and no bus went away but the idle was very rough and the guages are not working. Water and volt guages don't move and gas and oil go full over. Code P0505 showed up and I replaced the IAC. Worked fine until I turned it off and when I restarted they same guage issues returned and the rough idle. I put the new IAC in my Jeep (same engine) and it worked fine.
I checked all 4 wires from PCM to IAC and they all have the same resistance so I don't think it is a short in those wires.
What else can this be?

 

Bad replacement PCM.

Welcome to DF! Post down in the Dakota section, should get some good help there.

 

I'm going to move your post to the 2nd gen Dakota section. But before I do that, here is some information. For P0505 code
PCM (IAC DRIVER #1)
PCM (IAC DRIVER #2)
PCM (IAC DRIVER #3)
PCM (IAC DRIVER #4)
IAC INTERNAL FAILURE
IAC MOTOR DRIVER CIRCUIT SHORT TO VOLTAGE
IAC MOTOR DRIVER CIRCUIT SHORTED TO GROUND
IAC MOTOR DRIVER CIRCUITS OPEN
PCM - IAC 12 VOLT DRIVER OPEN
PCM - IAC GROUND DRIVER OPEN
DTC NOT EQUAL TO FREEZE FRAME DTC
IAC MOTOR WIRING HARNESS INTERMITTENT
IAC MOTOR
IAC #1 DRIVER CIRCUIT SHORTED TO #2, #3, OR #4
IAC #2 DRIVER CIRCUIT SHORTED TO #3 OR #4
IAC #3 DRIVER CIRCUIT SHORTED TO #4
IAC #1 DRIVER CIRCUIT SHORTED TO GROUND
IAC #2 DRIVER CIRCUIT SHORTED TO GROUND
IAC #3 DRIVER CIRCUIT SHORTED TO GROUND
IAC #4 DRIVER CIRCUIT SHORTED TO GROUND
IAC #1 DRIVER CIRCUIT OPEN
IAC #2 DRIVER CIRCUIT OPEN
IAC #3 DRIVER CIRCUIT OPEN
IAC #4 DRIVER CIRCUIT OPEN
TEST ACTION APPLICABILITY
1 Turn ignition on.
With the DRB, read the DTC’s.
Is the DTC Specific Good Trip Counter displayed and equal to zero?
All
Yes ® Go To 2
No ® Go To 8
2 Turn the ignition off.
Disconnect the IAC motor harness connector.
Disconnect the PCM harness connector(s).
Measure the resistance of each IAC motor driver circuit between the IAC motor
harness connector and the PCM harness connector.
Is the resistance below 5.0 ohms for each measurement?
All
Yes ® Go To 3
No ® Repair the open IAC motor driver circuit
Perform Powertrain Verification Test VER-5.
3 Turn the ignition off.
Disconnect the IAC motor harness connector.
Disconnect the PCM harness connector(s).
Measure the resistance between ground and the each IAC motor driver circuit.
Is the resistance below 100.0 ohms for any of the measurements?
All
Yes ® Repair the IAC motor driver circuit(s) that measured below 5.0
ohms for a short to ground.
Perform Powertrain Verification Test VER-5.
No ® Go To 4
4 Turn the ignition off.
Disconnect the IAC motor harness connector.
Disconnect the PCM harness connector(s).
Remove the ASD relay from the PDC.
Connect a jumper wire between cavity 30 and cavity 87 of the ASD connector in the
PDC.
Turn the ignition on.
Measure the voltage of each IAC motor driver circuit.
Is the voltage above 1.0 volt for any of the measurements?
All
Yes ® Repair the IAC motor driver circuit that measured above 1.0 volt
for a short to voltage.
Perform Powertrain Verification Test VER-5.
No ® Go To 5
5 Disconnect the IAC motor harness connector.
With the DRBIIIt, actuate the 9IAC STEPPER MOTOR9.
Using a 12-volt test light connected to ground, check each IAC motor driver circuit for
at least 10 seconds.
Note: The test light should flash rapidly (flicker) during actuation.
Does the test light flicker for each IAC motor driver circuit?
All
Yes ® Go To 6
No ® Replace the powertrain control module.TEST ACTION APPLICABILITY
6 Disconnect the IAC motor harness connector.
With the DRBIIIt, actuate the 9IAC STEPPER MOTOR9.
Using a 12-volt test light connected to 12-volts, check each IAC motor driver circuit
for at least 10 seconds.
Note: The test light should flash rapidly (flicker) during actuation.
Does the test light flicker for each IAC motor driver circuit?
All
Yes ® Go To 7
No ® Replace the powertrain control module.
Perform Powertrain Verification Test VER-5.
7 If there are no possible causes remain replace the IAC motor. All
Repair
Replace the idle air control motor
Perform Powertrain Verification Test VER-5.
8 Turn the ignition on.
With the DRB, determine if the DTC matches freeze frame DTC.
Is DTC equal to freeze frame DTC ?
All
Yes ® Go To 9
No ® Repair the DTC with freeze frame data.
Perform Powertrain Verification Test VER-5.
9 Turn the ignition on.
With the DRB, read the Freeze Frame Data.
Try to duplicate the conditions in Freeze Frame.
Did the DTC specific good trips change to 0?
All
Yes ® Go To 10
No ® Go To 26
10 Ignition Off
Disconnect IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance between IAC #1 Driver circuit and
ground (B-).
Is the resistance below 5.0 ohms?
All
Yes ® Repair the IAC #1 Driver Circuit shorted to ground.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 11
11 Ignition Off
Disconnect IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance between IAC #2 Driver circuit and
ground (B-).
Is the resistance below 5.0 ohms?
All
Yes ® Repair the IAC #2 Driver Circuit shorted to ground.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 12
TEST ACTION APPLICABILITY
12 Ignition Off
Disconnect IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance between IAC Driver #3 and ground (B-).
Is the resistance below 5.0 ohms?
All
Yes ® Repair the IAC #3 Driver Circuit shorted to ground.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 13
13 Ignition Off
Disconnect IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance between IAC Driver #4 and ground (B-).
Is the resistance below 5.0 ohms?
All
Yes ® Repair the IAC #4 Driver Circuit shorted to ground.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 14
14 Start engine and let idle.
Disconnect the IAC Motor Connector.
Note: Check connectors - Clean/repair as necessary.
Using a Voltmeter, measure the voltage of the IAC #1 Driver Circuit.
Was the voltage over 5.0 volts at any time?
All
Yes ® Go To 15
No ® Go To 25
15 Start engine and let idle.
Disconnect the IAC Motor Connector.
Note: Check connectors - Clean/repair as necessary.
Using a Voltmeter, measure the voltage of the IAC #2 Driver Circuit.
Was the voltage over 5.0 volts at any time?
All
Yes ® Go To 16
No ® Go To 24
16 Start engine and let idle.
Disconnect the IAC Motor Connector.
Note: Check connectors - Clean/repair as necessary.
Using a Voltmeter, measure the voltage of the IAC #3 Driver Circuit.
Was the voltage over 5.0 volts at any time?
All
Yes ® Go To 17
No ® Go To 23
17 Start engine and let idle.
Disconnect the IAC Motor Connector.
Note: Check connectors - Clean/repair as necessary.
Using a Voltmeter, measure the voltage of the IAC #4 Driver Circuit.
Was the voltage over 5.0 volts at any time?
All
Yes ® Go To 18
No ® Go To 22

TEST ACTION APPLICABILITY
18 Ignition Off
Disconnect IAC Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Note: The following steps are checking for a short between the IAC Driver
Circuits.
Using an Ohmmeter, measure the resistance between the IAC #1 Driver circuit and
#2, #3, #4 Driver circuits.
Is the resistance below 5.0 ohms on any of the Drivers?
All
Yes ® Repair the IAC Driver Circuits shorted together.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 19
19 Ignition Off
Disconnect the IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Note: The following steps are checking for a short between the IAC Driver
Circuits.
Using an Ohmmeter, measure the resistance between the IAC #2 Driver circuit and
#3, #4 Driver circuits.
Is the resistance below 5.0 ohms on any of the Drivers?
All
Yes ® Repair the IAC Driver Circuits shorted together.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 20
20 Ignition Off
Disconnect IAC Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Note: The following steps are checking for a short between the Driver
Circuits.
Using an Ohmmeter, measure the resistance between the IAC #3 Driver circuit and
#4 Driver circuit.
Is the resistance below 5.0 ohms?
All
Yes ® Repair the IAC Driver Circuits shorted together.
Perform the Powertrain Verification Test - Ver 5.
No ® Go To 21
21 If there are no possible causes remaining, replace the Idle Air Control Motor.
View repair options.
All
Repair
Replace the Idle Air Control Motor.
Perform Powertrain Verification Test VER-5.TEST ACTION APPLICABILITY
22 Ignition Off
Disconnect the IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance of the IAC #4 Driver Circuit from the
IAC Motor Connector to the PCM Connector.
Is the resistance below 5.0 ohms?
All
Yes ® Replace the Powertrain Control Module.
Perform the Powertrain Verification Test - Ver 5.
No ® Repair the open IAC Driver Circuit.
Perform the Powertrain Verification Test - Ver 5.
23 Ignition Off
Disconnect the IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance of the IAC #3 Driver Circuit from the
IAC Motor Connector to the PCM Connector.
Is the resistance below 5.0 ohms?
All
Yes ® Replace the Powertrain Control Module.
Perform the Powertrain Verification Test - Ver 5.
No ® Repair the open IAC Driver Circuit.
Perform the Powertrain Verification Test - Ver 5.
24 Ignition Off
Disconnect the IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance of the IAC #2 Driver Circuit from the
IAC Motor Connector to the PCM Connector.
Is the resistance below 5.0 ohms?
All
Yes ® Replace the Powertrain Control Module.
Perform the Powertrain Verification Test - Ver 5.
No ® Repair the open IAC Driver Circuit.
Perform the Powertrain Verification Test - Ver 5.
25 Ignition Off
Disconnect the IAC Motor Connector.
Disconnect the Powertrain Control Module connectors.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance of the IAC #1 Driver Circuit from the
IAC Motor Connector to the PCM Connector.
Is the resistance below 5.0 ohms?
All
Yes ® Replace the Powertrain Control Module.
Perform the Powertrain Verification Test - Ver 5.
No ® Repair the open IAC Driver Circuit.
Perform the Powertrain Verification Test - Ver 5.TEST ACTION APPLICABILITY
26 Start engine.
With the DRB in Systems Test, perform the IAC Wiggle Test.
Note: The idle speed should raise and lower with the display.
Wiggle the Wiring Harness from the IAC Motor to the PCM.
Observe for the IAC Motor to stop operating.
Did the IAC Motor stop operating at any time?
All
Yes ® Repair the Harness or Connectors as necessary.
Perform Powertrain Verification Test VER-5.
No ® Test Complete.

I love copy and paste

 

I think what he is saying is yes the PCM is getting fried but what caused it to die to begin with find the problem first then your PCM will survive.

Their is an underlying cause/problem you will just keep burning every new PCM up until you find the real problem.

 

Wow, that is a lot to test, but it has to be done. I have been able to pull up on the C1 connector at the PCM and everything works fine until I let go. Also, when I do get it running right and the gauges are working the problem returns if I turn it off and start it again.
The intermittent success of the PCM doesn't seem like a short, but I know it is not always the case. The PCM is under warranty so I am going to replace it while I can and I will start testing the circuits while I wait. I pulled the IAC, TPS, CKP, CSP sensors and tested them on my jeep with the same engine and they all worked, no codes. I have not pulled the governor pressure sensor. I did check the voltage at the 5v sensors and I am getting 4.7v at each sensor and 4.7v is coming out at the PCM.
I am not sure I know how to do the Powertrain verification test, can you give me a little more about this.
By the way, this all started when my son was trying to pull a friend out of the mud. He pulled hard a few times and decided he could not get him out so he turned off the engine to unhook and then tried to start and that is when the no bus appeared. We tried for 2 days to get it to start but nothing. When I replaced the PCM it started but threw the IAC code. The no bus has not reappeared, but the gauges don't work unless I pull up on the PCM connector.